The present invention relates to a method and an apparatus for inspecting defects, capable of inspecting defects such as foreign objects, shape failures and scratches on a substrate to be inspected, e.g., a semiconductor wafer, with high sensitivity by using light or a charged particle beam.
In a defect inspecting apparatus, optical inspection and SEM inspection both include pluralities of conditions: a deflection condition, a wavelength region and the like for the former, and an acceleration voltage, a beam current, the number of scanning times and the like for the latter. Depending on combinations thereof, the number of settable conditions even reaches several tens. One among these conditions is selected to provide highest inspection sensitivity, and then inspection is carried out.
As the conventional art regarding a method of setting optical or charged particle conditions in the defect inspecting apparatus, technologies described in JP-A-12-161932 (conventional art 1) and JP-A-2000-193594 (conventional art 2) have been known.
The conventional art 1 includes means for irradiating a substrate surface having a circuit pattern formed with light, or light and a charged particle beam, means for detecting a signal generated from the substrate, means for converting the signal detected by the detecting means into an image and temporarily storing the image, means for comparing a region of the stored image with another region having an identical circuit pattern formed, inspecting means for determining defects on the circuit pattern based on a result of the comparison, and a region for displaying operation contents or input contents on operation screens for inspection and inspection condition setting. In this case, a screen hierarchy is set for displaying the operation screens in parallel, and an inspection condition is decided by using the screen hierarchy.
The conventional art 2 is directed to a circuit pattern inspecting method designed to detect pattern defects by irradiating a substrate surface having a circuit pattern formed with light or a charged particle beam, detecting a signal generated from the substrate surface by the irradiation, storing the detected signal as a digital image, comparing the stored image with an image expected to be identical thereto to extract a difference, and then displaying the difference extracted based on the comparison. In this case, an image of a region specified on the substrate surface is detected and stored as a digital image. For the stored digital image, comparison is made once or a plurality of times by changing conditions to extract a difference. A condition of comparison that enables a difference to be extracted is searched by determining a proper image processing condition based on a result of the extraction. The searched condition is stored. Then, by using the stored condition, a defect is extracted based on comparison, and an image of a defect portion extracted by the comparison is displayed.
As described in the above conventional art, in the defect inspecting apparatus, in inspection, a number of test conditions including optical system conditions for obtaining an image and an image processing parameter for detecting defects from the obtained image are generally set to be optimal for each target for inspection as shown in FIG. 13.
First, in the defect inspecting apparatus, a given optical system condition is set (S1301). An optical image is detected from a pattern to be inspected with particularly high sensitivity under the set optical system condition (S1302). The detected optical image is displayed on displaying means, and a user visually verifies whether contrast or brightness of the displayed optical image is sufficient or not (S1303). These steps are repeated a plurality of times while changing the optical system conditions. A plurality of optical system conditions are present and, if combinations thereof are included, the number thereof becomes enormous. Thus, the user narrows down the optical system conditions to a plurality of test conditions having sufficient contrast and brightness of the optical image (S1304). Then, an image processing parameter is set (S1305), and test inspection is carried out in a small region (S1306). Then, for each detected defect candidate, verification is made as to whether the defect is one to be originally detected, or it was erroneous detection (S1307). These steps are carried out for all the selected test conditions (S1308), and one optical system condition having a largest number of detected defects and least erroneous detection is decided (S1309).
Subsequently, similarly to the optical system condition, the image processing parameter is set all over again (S1310), and test inspection (S1311) and detection rate checking (S1311) are repeated until sensitivity becomes sufficient (S1313). Then, after an optimal image processing condition is set, inspection is carried out (S1314).
In the above-described method of setting test conditions (inspection conditions), the process is basically sensual evaluation by the visual verification of the user. Consequently, a rule of thumb or skills are necessary, and individual differences occur in setting results. Furthermore, when the test conditions are narrowed down, the test conditions for realizing high sensitivity are not necessarily included. Since setting of the test conditions and the visual verification are repeated, binding hours for test condition setting become enormous for the user.